The proposed work seeks to increase our understanding of the structure-function and biosynthesis of hemoglobin. The hemoglobin system of the feline is of special interest. The work includes: 1. Determination of structures of the four components HbB1, HbB11, HbB and HbA found in domestic cat blood, and a study of their properties to develop an understanding of the basis for the physico-chemical and physiological peculiarities of these proteins. 2. Studies on regulatory mechanisms in the feline erythrocyte that control the level of DPG, ATP and other effectors, as well as the switch-over in the production of hemoglobin components. 3. Investigation of genetic and biosynthetic mechanism(s) that account for the production of variable proportions of DPG sensitive and insensitive hemoglobins (HbA and HbB) in different cats.